The present invention relates to power conversion apparatus and methods, and more particularly, to power conversion apparatus and methods for use, for example, in redundant power supply systems such as uninterruptible power supplies (UPSs)
UPSs are commonly used to provide power to critical equipment, such as computers, medical devices, telecommunications network components and the like. A UPS can provide conditioned, reliable power to such devices in the presence of AC utility failure or degradation conditions, such as blackout or brownout.
Many UPSs use an on-line configuration comprising an input rectifier circuit that receives an AC voltage from an AC power supply (e.g., an AC utility line) and that generates positive and negative DC voltages on DC voltage busses (or xe2x80x9crailsxe2x80x9d), and an output inverter circuit that generates an AC output voltage from the DC voltages on the DC busses. A commonly used output inverter configuration is the half-leg inverter, which typically includes first and second switches that selectively couple an output inductor to the positive and negative DC busses. In many such UPSs, an auxiliary DC power source, such as a battery coupled to the busses through a battery converter circuit, generates DC voltages on the busses in the event the AC power source fails and/or is degraded in quality.
The battery converter is sometimes unidirectional, i.e., it allows power to flow from the battery to the DC busses, but does not allow power flow from the DC busses back to the battery. When load current delivered by an inverter circuit contains insignificant DC content, such a UPS typically is stable, i.e., the positive and negative DC voltages on the DC busses can be controlled. However, when the output current has a significant DC component, such as may occur when driving a half-wave load or when energizing a magnetic device, the voltage on one of the DC busses may rise to undesirably high levels. This can result in component damage and/or failure.
According to some embodiments of the invention, a power conversion apparatus, such as an uninterruptible power supply (UPS), includes an input port, an output port, and first and second busses. An output circuit, for example, a half-leg inverter circuit, is coupled to the first and second busses and to the output port and is operative to transfer power therebetween. An auxiliary DC voltage generator circuit, for example, a battery converter circuit, is operative to generate DC voltages on the first and second busses. A multifunction rectifier circuit is coupled to the input port and to the first and second busses. The multifunction rectifier circuit is operative to generate DC voltages on the first and second busses from an AC power source at the input port when the apparatus is operating in a first mode, e.g., an AC powered operational mode. The multifunction rectifier circuit is operative to control relative magnitudes of the DC voltages generated by the auxiliary DC voltage generator circuit when the apparatus is operating in a second mode, e.g., a battery-powered operational mode.
In some embodiments of the invention, the multifunction rectifier circuit comprises an inductor having first and second terminals, a first switch operative to couple and decoupled the first voltage bus to and from the first terminal of the inductor, and a second switch operative to couple and decouple the second voltage bus to and from the first terminal of the inductor. The multifunction rectifier circuit further includes a third switch operative to couple the second terminal of the inductor to the input port in a first switch state and to couple the second terminal of the inductor to a reference voltage bus for the first and second busses in a second switch state. In some embodiments, the third switch is operative to couple the second terminal of the inductor to a phase terminal of the input port in the first switch state and to couple the second terminal of the inductor to a neutral terminal of the input port in the second switch state.
In further embodiments, the multifunction rectifier circuit is operative to selectively control relative magnitudes of the DC voltages generated by the auxiliary DC voltage generator circuit when the apparatus is operating in the second mode. For example, the multifunction rectifier circuit may commence controlling relative magnitudes of the DC voltages generated by the auxiliary DC voltage generator circuit responsive to at least one voltage on at least one of the first and second busses meeting a predetermined criterion, such as excursion beyond a maximum voltage magnitude.
The invention can provide several benefits. For example, in UPS applications, a power converter circuit according to embodiments of the invention can provide a mechanism for controlling voltage excursions on intermediate DC busses during battery-powered operation by using a dual-purpose AC input rectifier circuit that acts as a xe2x80x9cbalancerxe2x80x9d during battery-powered operation, and that generates DC voltages on the DC busses under normal, AC-powered operation. This can allow for the use of a unidirectional battery converter circuit and can obviate the need for additional regulating circuitry to control voltage excursions on the DC busses. By selectively using the xe2x80x9cbalancer,xe2x80x9d desired trade-offs between efficiency and stability can be achieved. The invention may be embodied as apparatus and methods.